The present invention generally relates to thin-film manufacturing techniques and, more specifically, to a self-aligning fabrication process used to produce thin-film mandrel structures useful for electroforming ink-jet pen components.
As is well-known to persons skilled in the art, many publications describe the details of common techniques used in thin-film fabrication processes. Reference to general texts, such as Silicon Processing for the VLSI Era by Stanley Wolf and Richard Tauber, copyright 1986, Lattice Press publishers, and VLSI Technology, S. M. Sze editor, copyright 1986, McGraw-Hill publishers (each incorporated herein by reference in applicable parts), is recommended, as those techniques can be generally used in the present invention. Moreover, the individual steps of such processes can be performed using commercially available integrated circuit fabrication machines.
The art of ink-jet technology is also relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines employ ink-jet technology to produce hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions, incorporated herein by reference. The state of the art is continually developing to improve the quality of the fundamental dot matrix form of printing intrinsic to ink-jet technology. Current products have achieved print densities of up to 1200 dots-per-inch ("DPI"), achieving print quality comparable to the more expensive laser printers. To that end, thin-film technology has been employed to produce precision components such as orifice plates, fine mesh ink filters, and the like, for ink-jet pens.
For example, ink-jet pens can utilize an orifice plate generally formed on a thin-film mandrel. The mandrel can consist of a glass plate coated with a conductive film. Non-conductive discs are defined on the surface of the conductive film for determining the location and size of the orifices. Generally, the discs are about three times the diameter of the target hole size. The orifice size is determined by carefully controlling the electroplating parameters (current, timing, and the like) for forming an orifice plate on the mandrel. Therefore, a variation in these parameters will directly affect the size of the orifices. Moreover, if a thicker orifice plate is needed, it is necessary to increase the disc size. Manufacturing tolerances limit such disc dimensioning, resulting in a decreased orifice diameter if the thickness of the orifice plate increases over the disc size tolerance.
A standard manufacturing process for producing mandrel structures used for electroforming ink-jet components is shown in FIG. 1 (Prior Art). The process begins with a commercially available dielectric substrate 102, such as a silicon dioxide wafer or a transparent glass (FIG. 1A). As is known in the art, such wafers have a highly polished, flat surface 104. To insure proper adhesion, the surface 104 is cleaned and then a thin-film of metal 106, such as stainless steel, is deposited across the surface 104, forming a new surface 108 (FIG. 1B). A dielectric film 110 is deposited on the surface 108 of the metal layer 106 (FIG. 1C). Next, the dielectric layer 110 is covered with a photoresist 112 (FIG. 1D). The photoresist 112 is masked and developed to a desired pattern (FIG. 1E). The dielectric layer 110 is then etched (FIG. 1F). The patterned structure, for example, disk constructs 116, can now serve as a mandrel structure for forming a workpiece (FIG. 1G). As shown in FIG. 1H, a metal workpiece 118 is electroformed on the surface 108 of the metal layer 106. During electroforming, metal is initially deposited onto the conductive areas of the structure; that is, onto the metal layer surface 108, but not onto dielectric disk constructs 116. However, as the deposited metal thickness increases, the metal flows and partially plates over the disk constructs 116. When the workpiece 118 reaches the predetermined proper thickness or proper dimensions, the plating is stopped and the electroformed workpiece 118 is removed from the mandrel structure (FIG. 1I). In actual practice, a plurality of workpieces are formed on each substrate.
Examples of other processes are disclosed in U.S. Pat. Nos. 4,773,971 (Lam et al.)(assigned to the common assignee of the present invention), 4,954,225 and 4,839,001 (Bakewell) and 4,229,265 (Kenworthy).
There are several drawbacks to using the mandrel structure formed by these conventional prior art processes. Any defects in the dielectric layer, such as a stray particle, a pinhole, or any edge roughness in the pattern, will replicate as a defect in the electroformed workpiece 118. In fact, the electroforming process will inherently magnify any defect of the mandrel in the workpiece 118.
Generally, such methods of forming mandrels of a dielectric require critical alignment for the exposure process steps. A misaligned mandrel will result in an asymmetrical and offset orifice when the construct is used as a mandrel. If a second exposure process for forming the mandrels is used in a particular fabrication, the alignment between the two features so formed is absolutely critical. Thus, variations of such processes may call for more than one such critical alignment. Even small errors can negatively impact the electroforming process yield since many components are formed on one wafer.
Another problem is that if the mandrel size is fixed or otherwise constrained in size by the need to achieve a certain packing density, the electroform thickness and the dimensions of the electroformed part can not be controlled independently. The final shape of the workpiece is controlled by the physics of the electroforming steps of the process.
Therefore, there is a need for an improved thin-film process to form thin-film structures such as a mandrel structure or pattern of mandrels.